Connecting techniques for stacked CMOS devices

ABSTRACT

A stacked integrated circuit includes multiple tiers vertically connecting together. A multi-layer horizontal connecting structure is fabricated inside a substrate of a tier. Layers of the horizontal connecting structure have different patterns as viewed from above the substrate.

BACKGROUND

A stacked CMOS chip is a kind of integrated circuit having multipledevice tiers which are vertically stacked and which share one package.Stacked CMOS chips extend chip structure to three dimensions andincrease the number of CMOS devices that can be “squeezed” into a givenfootprint.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a perspective-sectional view of a stacked CMOS devicein accordance with some embodiments.

FIG. 2 illustrates a perspective-sectional view of a stacked CMOS devicein accordance with some alternative embodiments.

FIG. 3 and FIG. 4 illustrate perspective-sectional views of a three-stepstructure of a horizontal connecting structure and a four-step structureof a horizontal connecting structure.

FIG. 5 illustrates a flow diagram of some embodiments of methods forconnecting stacked CMOS devices.

FIGS. 6a-6e illustrate perspective-sectional views of some embodimentsof methods for connecting stacked CMOS devices.

DETAILED DESCRIPTION

The description herein is made with reference to the drawings, whereinlike reference numerals are generally utilized to refer to like elementsthroughout, and wherein the various structures are not necessarily drawnto scale. In the following description, for purposes of explanation,numerous specific details are set forth in order to facilitateunderstanding. It will be appreciated that the details of the figuresare not intended to limit the disclosure, but rather are non-limitingembodiments. For example, it may be evident, however, to one of ordinaryskill in the art, that one or more aspects described herein may bepracticed with a lesser degree of these specific details. In otherinstances, known structures and devices are shown in block diagram formto facilitate understanding.

Relative to packaging solutions where multiple chips are arranged inseparate horizontally spaced packages, stacked CMOS devices (whichinclude multiple chips that are vertically “stacked” over one another ina single package), shrink the lateral footprint for the circuits whenarranged within a product. However, the vertical dimension of stackedCMOS devices can become an issue in some applications. For example,stacked CMOS chips can be too thick for some ultra-thin apparatuses,such as cell phones or portable entertainment units. In addition,forming electrical connections between different vertical device tiersrequires alignment of corresponding contact points on the correspondingdevice tiers, which limits flexibility in structure design. Therefore,in a stacked semiconductor integrated circuit in accordance with someembodiments, instead of connecting multiple tiers solely by a verticalinterwafer via, a multi-layer horizontal connecting structure isfabricated inside a substrate of an individual device tier. Individuallayers of the multi-layer horizontal connecting structure have differentpatterns as viewed from above the substrate. Relative to conventionalapproaches, stacked CMOS devices with multi-layer horizontal connectingstructures provide several advantages. For example, locations ofelectrical contact points of different tiers are flexible, metal usagefor electrical path layers is reduced, and the number of and/orthickness of electrical path layers is decreased which tends to “thindown” chip thickness. Power dissipation is also reduced.

FIG. 1 illustrates a perspective-sectional view of a stacked CMOS device100 in accordance with some embodiments. The stacked CMOS device 100includes multiple device tiers, such as a first device tier 102 and asecond device tier 116. The first device tier 102 comprises a firstsubstrate 104 and a first plurality of devices 106. The second devicetier 116 comprises a second substrate 118 and a second plurality ofdevices 120. A first inter-tier horizontal interconnecting structure 108is formed at least partially inside the first substrate 104. The firstinter-tier horizontal structure 108 electrically connects one or moredevices, such as device 106, on the first substrate 104, to one or moredevices, such as device 120, on the second substrate 118. The firstinter-tier horizontal interconnecting structure 108 can comprisesmultiple conductive layers, such as metal layers, with differentpatterns as viewed from above the first substrate.

The first inter-tier horizontal structure 108 includes a firstconductive layer 110, which takes the form of a vertical connectionelement in this example. The first conductive layer 110 is coupled to asecond conductive layer 112, which takes the form of a first horizontallayer in this example. The second conductive layer 112, which takes theform of a first horizontal layer in this example, is disposed above thefirst vertical connection element 110 and is connected to a device ofthe first plurality of devices 106 or other contact paths on the firstdevice tier 102, for example, power, ground or signal pins. The secondconductive layer 112 is electrically coupled to the device of the seconddevice tier 116 by the first vertical connection element 110. The firstconductive layer 110 couples the second conductive layer 112 (and hencedevice 106) to an electrical interconnect structure 115 on the seconddevice tier 116. The electrical interconnect structure 115 has multiplemetal layers, such as 113 and 114. These metal layers 113 and 114 arearranged under a back side of the first substrate 104 and are coupled toa device 120 of the second device tier 116. The electrical interconnectstructure 115 can also be coupled to other contact points of the seconddevice tier 116 stacked under the first device tier 102. The electricalinterconnect structure 115 can either be formed in a dielectric layerbetween the first tier 102 and the second tier 116 or can be coupledinto the second tier 116.

The first plurality of devices 106 on the first substrate 104 and thesecond plurality of devices 120 on the second substrate 118 can be twodimensional structures (e.g., planar MOSFETs) or three dimensionsstructures (e.g., silicon on insulator (SOI) devices or FinFET devices).The first inter-tier horizontal interconnecting structure 108 in thefirst substrate 104 can be copper, silver, tungsten or aluminum with aTa, Ti, TaN, TiW, TiWN or TiN barrier for preventing metal diffusions. Adielectric layer is formed surrounding the barrier layer for electricalisolation. The first substrate 104 can be either bulk Silicon orepitaxial Silicon on a dielectric material. To further reduce metalmaterial, reduce layers, or decrease complexity of the electricalinterconnect structure 115, the first device tier 102 can have deviceson both sides. The first device tier 102 can also be “flipped” overrelative to what is shown in FIG. 1 so that a top side of the firstsubstrate 104 with the first plurality of devices 106 is proximate to atop side of the second substrate 118 with the second plurality ofdevices 120. In such way, electrical connections between the firstplurality of devices 106 and the second plurality of devices 120 becomemore flexible. The first device tier 102 can be formed onto the seconddevice tier 116 by deposition, spray coated, curtain coated, or spincoated. The first device tier 102 can also be bonded to the seconddevice tier 116.

Thus, FIG. 1 shows an example of a stacked CMOS device 100 with twodevice tiers (e.g., 102, 116) connected by a multi-layer inter-tierhorizontal interconnecting structure 108 in accordance with someembodiments. Some advantages of this structure include improvedplacement and routing flexibility and reduced metal usage and furtherreduction of area and power consumption of the circuit.

FIG. 2 illustrates a perspective-sectional view of a stacked CMOS device200 in accordance with some alternative embodiments. The stacked CMOSdevice 200 shows example embodiments of disclosure that a third devicetier 226 with a third substrate 228 and a third plurality of devices(e.g., 232) can be stacked onto a first device tier 202 and a seconddevice tier 216 similar to 102 and 116 in FIG. 1. More tiers can bestacked onto the third device tier 226. A second horizontal connectingstructure 230 inside the third substrate 218 comprises three layers 220,222 and 224 and electrically connects the first device tier 202 and thethird device tier 226 of which a detailed example perspective-sectionalview is shown in FIG. 3. Notably, the first substrate 204 with the firsthorizontal connecting structure and the third substrate 228 with thesecond horizontal connecting structure can have similar or differentstructure. Horizontal connecting structures can have same or differentnumbers of conductive layers. Patterns of conductive layers can also bedifferent. Thus, FIG. 2 shows another example semiconductor integratedcircuit with more than two device tiers connected by multi-layerinter-tier horizontal interconnecting structures in accordance with somealternative embodiments.

FIG. 3 illustrates a perspective-sectional view of an examplethree-layer structure of a horizontal connecting structure. Thehorizontal connecting structure can be used as either the firsthorizontal connecting structure 208 or the second horizontal connectingstructure 230 in FIG. 2. In the example, a first conductive layer 320 isa first vertical connection element electrically coupled to a device ofa device tier thereunder. A second conductive layer 322 is a firsthorizontal layer disposed above the first vertical connection element320 and a third conductive layer 324 is a second horizontal layerdisposed above the first horizontal layer 322 and electrically coupledto a device on a substrate 304 of a device tier 326 thereon through boththe first conductive layer 320 and the second conductive layer 322. Alocation of at least a portion of the first conductive layer 320 shiftshorizontally to a location of the second conductive layer 322 or thethird conductive layer 324. The first conductive layer 320 connectscontact points such as 326 and 328 on the other side of a substrate 304not vertically aligned with a location of the first conductive layer 320through the second conductive layer 322 and the third conductive layer324. The first conductive layer 320, which is a vertical connectionelement in the illustrated example, can have a square-like or roundedperimeter as viewed from above and can fall within edges of secondconductive layer. In some embodiments, 320 is formed along Z direction,322 is formed along Y direction, 324 is formed along X direction. Insome embodiments, 320, 322, 324 are in perpendicular with each other inrespective X, Y, Z direction. In some embodiments, 304 includes anynumber of conductive layers. In some embodiments, any two conductivelayers of the conductive layers in 304 are in parallel or inperpendicular with each other.

FIG. 4 illustrates a perspective-sectional view of a four-layerhorizontal connecting structure 400 comprising an additional fourthconductive layer. The four layer horizontal connecting structure 400 canbe used as either the first horizontal connecting structure 208 or thesecond horizontal connecting structure 230 in FIG. 2. In FIG. 4'sexample, a first conductive layer 420 is a first vertical connectionelement extending in the z-direction and which is electrically coupledto a device of a device tier (not shown) thereunder. A second conductivelayer 422 is a first horizontal layer disposed above the first verticalconnection element 420 and extending in the y-direction. A thirdconductive layer 423 is a second vertical connection element connectingthe second conductive layer 422 to a fourth conductive layer 424. Thefourth conductive layer 424 is a second horizontal layer which extendsin the x direction and which is disposed above the second verticalconnection element 423. The first conductive layer 420 is electricallycoupled to a device on a substrate 404 of device tier 426 through thesecond conductive layer 422, the third conductive layer 423, and thefourth conductive layer 424. Structures of FIG. 3 and FIG. 4 can beapplied to any upper level tier (e.g. the tier 102 of 100 and tier 202or 226 of 200) of disclosed stacked CMOS devices.

FIG. 5 illustrates a flow diagram of some embodiments of methods forconnecting stacked CMOS tiers in accordance with some embodiments. Whiledisclosed methods (e.g., methods 500 of FIG. 5) are illustrated anddescribed below as a series of acts or events, it will be appreciatedthat the illustrated ordering of such acts or events are not to beinterpreted in a limiting sense. For example, some acts may occur indifferent orders and/or concurrently with other acts or events apartfrom those illustrated and/or described herein. In addition, not allillustrated acts may be required to implement one or more aspects orembodiments of the description herein. Further, one or more of the actsdepicted herein may be carried out in one or more separate acts and/orphases.

At 502, a first device tier with a first substrate including a firstplurality of devices is formed.

At 504, a second substrate is applied on the first device tier.

At 506, a first conductive layer is formed in the second substrateelectrically connecting to a device on the first substrate.

At 508, a second conductive layer is formed in the second substrate.

At 510, a second plurality of devices and electrical connections areformed on the second substrate.

One example of FIG. 5's method is now described with regards to a seriesof cross-sectional views as shown in FIGS. 6a-6e . Although 6 a-6 e aredescribed in relation to method 500, it will be appreciated that thestructures disclosed in FIGS. 6a-6e are not limited to such a method,but instead may stand alone as a structure.

At FIG. 6a , a first device tier 602 with a first substrate 618 and afirst plurality of devices is formed. An electrical path 615 withmultiple layers of metal is formed onto the first substrate inside adielectric layer 630. The multiple layers of metal can be copper,silver, tungsten or aluminum, for example.

At FIG. 6b , a second substrate 604 is applied on the first device tier602. The second substrate can be formed by deposition, such as epitaxialdeposition for example, or can be bonded to the second device tier 116.For example, in some embodiments, the first device tier can correspondto a first bulk silicon wafer, and the second device tier can correspondto a second bulk silicon wafer, wherein the first wafer has a backside(or topside) that is bonded to the topside of the second bulk siliconwafer.

At FIG. 6c , after the second substrate has been applied to the firstsubstrate, a first conductive layer 610 is formed in the secondsubstrate. The first conductive layer 610 electrically connecting to adevice on the first substrate 618. For example, the first conductivelayer 610 can be copper, silver, tungsten or aluminum with a Ta, Ti,TaN, TiW, TiWN or TiN barrier (not shown) for preventing metaldiffusions. A dielectric layer (not shown) is formed surrounding thebarrier layer for electrical isolations.

At FIG. 6d , a second conductive layer 612 is formed in the secondsubstrate 604. For example, the second conductive layer 612 can becopper, silver, tungsten or aluminum with Ta, Ti, TaN, TiW, TiWN or TiNbarrier for preventing metal diffusion, and also form dielectric layersurrounding the barrier layer for electrical isolation.

At FIG. 6e , a second plurality of devices and electrical connectionsare formed on the second substrate. One or more of the second pluralityof devices on the second substrate are electrically coupled to one ormore of the first plurality of devices on the first substrate.

Thus, some embodiments relate to a semiconductor integrated circuit(IC). The semiconductor integrated circuit comprises a first device tierwith an first inter-tier horizontal interconnecting structure inside afirst substrate and a second device tier being electrically connected tothe first device tier by the first inter-tier horizontal interconnectingstructure. The first inter-tier horizontal interconnecting structurecomprises a first conductive layer and a second conductive layer withdifferent patterns.

Other embodiments relate to an integrated circuit. The integratedcircuit comprises a first substrate including a first plurality ofdevices and a first horizontal interconnecting structure disposed in thefirst substrate. The integrated circuit further comprises a secondsubstrate including a second plurality of devices, the first and secondsubstrates being electrically connected to one another so the secondsubstrate is under the first substrate and the first horizontalinterconnecting structure electrically couple one or more of the firstplurality of devices to one or more of the second plurality of devices.The first horizontal interconnecting structure comprises a firstconductive layer and a second conductive layer with different patternsas viewed from above the first substrate.

Still another embodiment relates to a method of fabricating stacked CMOSdevices. In this method, a first device tier with a first substrateincluding a first plurality of devices is formed. A second substrate isapplied on the first device tier. A first conductive layer is formed inthe second substrate electrically connecting to a device on the firstsubstrate. A second conductive layer is then filled in the secondsubstrate. At last, a second plurality of devices and electricalconnections are formed on the second substrate.

It will be appreciated that while reference is made throughout thisdocument to exemplary structures in discussing aspects of methodologiesdescribed herein (e.g., the structure presented in FIGS. 6a-6e , whilediscussing the methodology set forth in FIG. 5), that thosemethodologies are not to be limited by the corresponding structurespresented. Rather, the methodologies (and structures) are to beconsidered independent of one another and able to stand alone and bepracticed without regard to any of the particular aspects depicted inthe FIGS. Additionally, layers described herein, can be formed in anysuitable manner, such as with spin on, sputtering, growth and/ordeposition techniques, etc.

Also, equivalent alterations and/or modifications may occur to thoseskilled in the art based upon a reading and/or understanding of thespecification and annexed drawings. The disclosure herein includes allsuch modifications and alterations and is generally not intended to belimited thereby. For example, although the figures provided herein, areillustrated and described to have a particular doping type, it will beappreciated that alternative doping types may be utilized as will beappreciated by one of ordinary skill in the art.

In addition, while a particular feature or aspect may have beendisclosed with respect to only one of several implementations, suchfeature or aspect may be combined with one or more other features and/oraspects of other implementations as may be desired. Furthermore, to theextent that the terms “includes”, “having”, “has”, “with”, and/orvariants thereof are used herein, such terms are intended to beinclusive in meaning—like “comprising.” Also, “exemplary” is merelymeant to mean an example, rather than the best. It is also to beappreciated that features, layers and/or elements depicted herein areillustrated with particular dimensions and/or orientations relative toone another for purposes of simplicity and ease of understanding, andthat the actual dimensions and/or orientations may differ substantiallyfrom that illustrated herein.

What is claimed is:
 1. A semiconductor integrated circuit (IC),comprising: a first device tier comprising a first dielectric layerdisposed on a first semiconductor substrate, wherein a plurality ofmetal layers are disposed within the first dielectric layer and a firstinter-tier horizontal interconnecting structure is disposed inside thefirst semiconductor substrate, and a second device tier beingelectrically connected to the first device tier by the first inter-tierhorizontal interconnecting structure, wherein the first inter-tierhorizontal interconnecting structure comprises a first conductive layerand a second conductive layer disposed on the first conductive layerwith a different pattern than the first conductive layer.
 2. The IC ofclaim 1, wherein the first inter-tier horizontal interconnectingstructure comprises: a first vertical connection element disposed in thefirst semiconductor substrate and electrically coupled to a device ofthe second device tier, and a first horizontal layer disposed in thefirst semiconductor substrate above the first vertical connectionelement and laterally extending to a position that is not verticallyaligned with the first vertical connection element, wherein the firsthorizontal layer is electrically coupled to the device of the seconddevice tier through the first vertical connection element.
 3. The IC ofclaim 2, wherein the second device tier further comprises an electricalinterconnect structure arranged over the device of the second devicetier, the electrical interconnect structure having an upper surface towhich the first vertical connection element is coupled.
 4. The IC ofclaim 1, wherein the first inter-tier horizontal interconnectingstructure comprises, a first vertical connection element disposed in thefirst semiconductor substrate and electrically coupled to a device ofthe second device tier, a first horizontal layer disposed in the firstsemiconductor substrate above the first vertical connection element, anda second horizontal layer disposed in the first semiconductor substrateabove the first horizontal layer and being electrically coupled to thedevice through both the first vertical connection element and the firsthorizontal layer.
 5. The IC of claim 4, further comprising: a secondvertical connection element disposed in the first semiconductorsubstrate and electrically coupling the first horizontal layer to thesecond horizontal layer.
 6. The IC of claim 1, wherein the firstinter-tier horizontal interconnecting structure further comprises: athird conductive layer in the first semiconductor substrate and arrangedin parallel or in perpendicular with the second conductive layer.
 7. TheIC of claim 1, further comprising a third device tier being electricallyconnected to the first device tier by a second inter-tier horizontalinterconnecting structure.
 8. The IC of claim 1, the first device tierhas devices on both sides.
 9. An integrated circuit, comprising: a firstdevice tier comprising a first plurality of devices disposed on a firstsemiconductor substrate; a first horizontal interconnecting structuredisposed in the first semiconductor substrate, wherein the firsthorizontal interconnecting structure comprises a first conductive layerconnected to a second conductive layer, wherein the first conductivelayer and the second conductive layer have different patterns as viewedfrom above the first semiconductor substrate; a second device tiercomprising a second plurality of devices disposed on a secondsemiconductor substrate, the second semiconductor substrate is under thefirst semiconductor substrate; and wherein the first horizontalinterconnecting structure electrically couples one or more of the firstplurality of devices to one or more of the second plurality of devices.10. The integrated circuit of claim 9, wherein the first semiconductorsubstrate is deposited, spray coated, curtain coated, spin coated orbonded to the second semiconductor substrate.
 11. The integrated circuitof claim 10, further comprising: a third device tier stacked onto thefirst device tier comprising a third plurality of devices disposed on athird semiconductor substrate; and a second horizontal interconnectingstructure inside the third semiconductor substrate.
 12. The integratedcircuit of claim 9, further comprising a second semiconductor substrateincluding a second plurality of devices under the first semiconductorsubstrate wherein a first face of the first semiconductor substrate withdevices thereon faces a second face of the second semiconductorsubstrate with devices thereon.
 13. The integrated circuit of claim 9,wherein the first horizontal interconnecting structure is copper,silver, tungsten or aluminum.
 14. The integrated circuit of claim 9,wherein the first horizontal interconnecting structure comprises abarrier layer made of Ta, Ti, TaN, TiW, TiWN or TiN, and a dielectriclayer surrounding the barrier layer.
 15. The integrated circuit of claim11, wherein the first horizontal interconnecting structure and thesecond horizontal interconnecting structure have same or differentnumbers or patterns of conductive layers.
 16. A stacked CMOS device,comprising: a first device tier comprising a first device disposed overa first semiconductor substrate; a second device tier stacked over thefirst device tier and comprising a second device disposed over a secondsemiconductor substrate; and an interconnecting structure configured toelectrically connect the first device tier and the second device tier,which is disposed within the second semiconductor substrate and thatcomprises a first connection point at a lower surface of theinterconnecting structure facing the first device and a secondconnection point at an upper surface of the interconnecting structurefacing the second device, wherein the first connection point and thesecond connection point are not vertically aligned; wherein theinterconnecting structure comprises a first conductive layer extendinghorizontally to connect the first and second connection points.
 17. Thestacked CMOS device of claim 16, further comprising: a verticalconnection element extending into the second semiconductor substrate andphysically connecting the first connection point to an underlying metallayer disposed within a dielectric layer.
 18. The stacked CMOS device ofclaim 16, wherein the interconnecting structure further comprises: asecond conductive layer disposed above the first conductive layer andhaving a different pattern from the first conductive layer; wherein anupper surface of the second conductive layer is co-planed with an uppersurface of the second semiconductor substrate.
 19. The stacked CMOSdevice of claim 16, wherein the interconnecting structure furthercomprises: a second conductive layer arranged in parallel or inperpendicular with the first conductive layer as viewed from above thesecond semiconductor substrate and connected to the first conductivelayer through a vertical connection element disposed therebetween.